A granular material drainage tank is used in particular in a wet granulation plant in which a molten product is introduced into a powerful stream of water which solidifies, granulates and cools it. This operation is generally performed discontinuously in a granulating tank equipped for the injection of water of granulation. Once a batch of molten product has been poured into the granulation tank, and therefore granulated, the granular material/water mixture is pumped from the granulating tank to a drainage tank so that the granular material can be separated from the water of granulation.
Such a drainage tank generally comprises a cylindrical upper part and a conical lower part which ends in an outlet portion equipped with a shut-off member. The conical lower part is also equipped, upstream of the shut-off member, with a device for separating the water and the granular material, which comprises an annular collection chamber for the drained-off liquid and filtering surfaces separating the inside of the reservoir from the annular collection chamber. The upper part is fitted with a lid, fixed some distance from the upper edges of the upper part, so as to define a peripheral overflow slot. That represents a means of removing the excess liquid, to allow the excess water of granulation to be evacuated. A channel is arranged around the drainage tank to collect the overflowed water of granulation. The granular material/water mixture is conveyed to the tank by means of a filling line that passes through the lid. When the drainage tank is filled, the granular material is held back by the filtering surfaces, whereas the water is collected in the collection chamber. The excess, or overflow, water can flow through the means of evacuating excess liquid.
One disadvantage with such a drainage tank is that, depending on the way in which the granular material spreads out within the tank, streams of water at higher speeds can form. These streams of water at higher speeds cause greater overflowing at certain points around the periphery of the drainage tank, carrying with them fairly sizeable amounts of granular material. The overflowing of the excess water is therefore not uniform around the entire periphery of the drainage tank. In addition, the drainage tank is sometimes slightly inclined, and this further accentuates this problem of non-uniform overflow.
One problem addressed by the present invention is that of proposing a tank for draining a granular material/liquid mixture which allows the excess liquid to be removed more uniformly when the drainage tank is filled.